Research On Generation Method Of Surface Plasmon Polariton Vortex Field

Optical vortices are a special optical field with helical wavefront structure and phase singularities.The phase singularity is essentially caused by the spiral distribution of the wavefront of the optical field,because the spiral wavefront will causes the phase at the center to be uncertain.In recent decades,optical vortices have been widely used,and it has achieved a lot of good results in micro-nano manipulation,non-linear optics,biomedicine,optical communication and other fields now.Surface plasmon polariton(SPP)is an electromagnetic oscillation propagating along the metal surface which is produced by the interaction of free electrons on the metal surface with the incident optical field.SPP has some unique advantages in producing optical vortices because it can confine optical field to the interface between metal and medium,meanwhile break through the diffraction limit and produce higher field enhancement effect.Based on the existing theoretical basis,this paper will do some in-depth research to excavate a new method and optimize the existing method of surface plasmon vortex field.The main research contents are as follows:1.A circular ring distribution nano-cavity array which is used for exciting surface plasmon vortex field is studied.Starting from the two aspects of circularly polarized light and linearly polarized light,by using the research method of theoretical model analysis and simulation analysis,then make an intensive study for the conditions of surface plasmon vortex field excitation by the structure and the effects of these conditions on the excitation of surface plasmon vortex field in detail.2.A spiral-distributed nano-cavity array which is used for exciting surface plasmon vortex field is proposed.After introducing the helix distribution,the five parameters that can influence the SPP vortex field are the radius difference between the inner and outer nano-cavity arrays,the rotational velocity factor of the nano-cavity arrays,the number of segments of the helix,and the ratio of the pitch to the surface plasmon wavelength.Because there are many parameters that can be controlled,and each parameter will affect the final surface plasmon vortex field to varying degrees,so it is theoretically very convenient to generate SPP vortices with arbitrary topological charges by precise combination and arrangement.3.A multi-segment spiral slit structure which is used for exciting SPP compound vortex field is proposed.Firstly,the analytical expression of the SPP compound vortices field is deduced theoretically,and then verified by simulation software.Finally,it is shown that the SPP compound vortices field is actually formed by the superposition of two surface plasmon vortices with different topological charges.At the same time,the intensity of the optical field of the vortex field with smaller topological charge is weaker than that of the vortex field with larger topological charge.